1. Field of the Invention
This invention relates to an active-energy-ray-curable coating composition which can form a hard-coating layer which has excellent adhesiveness to plastic substrates, transparency, and hardwearing properties. Further, this invention relates to an active-energy-ray-curable coating composition which can form a coating film upon evaporation of the solvent through drying and then can be subjected to processing such as molding, printing and transfer before curing the film by active-energy-ray. The obtained cured article has an excellent hardwearing properties.
2. Discussion of the Background
Generally speaking, plastics, for example, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyvinylchloride, ABS resin and cellulose acetate are used for various fields due to their light weight, high workability, excellent impact resistance, etc. However, because of their poor surface hardness, these plastic products are liable to have surface flaws, so that it is difficult for them to be used in fields in which hardwearing properties is required. Thus, there is a demand for an active-energy-ray-curable hard coating material which imparts hardwearing properties to these plastic products.
Further, in some cases, a curable hard coating material can not be directly applied to the surface of the plastic product. Instead, it is applied to a separate substrate, such as a plastic film. Then, after such processes as printing or application of an adhesive layer have been performed on the surface of the plastic film as needed, the curable hard coating layer is transferred to the surface of the plastic product. In view of this, there is a demand for a coating composition which can form a curable coating film upon drying of the solvent, and then after irradiation with active-energy-ray, give a cured hardwearing coating.
Japanese Patent Publications No. 53-43553 and Japanese Patent Laid Open No. 50-82173 disclose an active-energy-ray-curable coating composition which forms a hardwearing coating on the plastic molded products. These coating materials contain (A) a multifunctional (meth)acrylate having at least three functional acryloyl groups, (B) organic solvent and (C) photopolymerization initiator. Further, Japanese Patent Laid Open No. 63-92675 discloses that a colloidal silica is added to these active-energy-ray curable coating composition to improve their hardwearing properties. Japanese Patent Laid Open No. 59-41366 discloses a coating hardenable resin composition comprising (a) poly((meth)acryloyloxyalkyl)isocyanurate compound, (b) urethane poly(meth)acrylate, (c) polymerisation initiator and (d) inorganic filler. Some of these active-energy-ray-curable hard coating materials give a coating film having excellent hardwearing properties. However, none of these films exhibit adhesiveness that would be acceptable to any type of plastic substrate. Under the circumstances, a primer has to be first coated on the surface of the plastic substrate, and then, the coating compositions are applied to this primer surface of the plastic substrates.
U.S. Pat. No. 5,378,735 discloses an ultraviolet-ray-curable composition composed of: (a) a compound obtained by reacting a silane coupling agent containing isocyanate groups with a multifunctional acrylate containing hydroxyl groups; (b) a multifunctional acrylate having at least three acryloyl groups in the molecule; (c) silica sol in an organic solvent; and (d) a photopolymerization initiator. This composition, however, exhibited a rather unsatisfactory adhesiveness when cellulose acetate was used as the substrate.
To improve the adhesiveness to plastic substrate, it might be possible to use a compound having one or more carboxyl groups and one (meth)acryloyl group in the molecule (as disclosed in Japanese Patent Laid Open No. 2-235909), as a component of the active-energy-ray-curable hard coating composition. However, using such a monofunctional (meth)acrylate results in a great reduction in the crosslinking density of the (meth)acryloyl groups of the coating, so that it is impossible to obtain a coating film having a satisfactory level of hardwearing properties.